The relative timing of the measurements made in an entanglement swapping experiment can be altered in a seemingly simple way, transforming the original Figure 4 geometry into the “delayed choice entanglement swapping” (DCES) configuration shown in Figure 5 [1]}, [2]}. Again, two pairs of entangled photons are created, and again Alice measures the left-most photon and Bob measures the right-most photon. Also, as before, the central two photons are measured in the standard Bell basis, using the same configuration as in Figure 4. The only difference is one of relative timing; in DCES, Alice and Bob make their measurements first, and the central Bell-basis measurement is made last.
